A multi-rotor flying object is generally a kind of helicopter having three or more rotors. The multi-rotor flying object may fly while changing a torque and a speed of the rotors and may be easily maintained and manipulated, as compared with a traditional single-rotor helicopter. Due to these advantages and the rapid development of an electronic technology, the multi-rotor flying object has been rapidly applied in various fields. In the past, military unmanned flying objects having a large size have been mainly used. However, recently, civil small unmanned flying objects have been mainly manufactured. The utilization of the small unmanned flying objects has variously increased from image photographing to transport of articles.
Among various types of small unmanned flying objects, a multi-rotor flying object called a quad-rotor has advantages more than those of other flying objects. The biggest advantage is that a mechanical mechanism is very simple. In the case of the quad-rotor, a trim does not need to be adjusted before flight, a mechanical vibration is not large, and the possibility that a component will be damaged due to fatigue is low. In addition, since it easy to mathematically model the quad-rotor due to a simple form, the quad-rotor is appropriate for automatic flight, and beginners may easily pilot the quad-rotor unlike other small flying objects requiring training for a long period of time in order to pilot the flying objects. Further, since the quad-rotor uses several small propellers, it is relatively safe for people unskilled in piloting or management. That is, everybody may easily pilot, maintain, repair, and manage the quad-rotor even though he/she does not have professional knowledge of a flying object or is not more trained in advance. Due to these advantages of the quad-rotor, an influence of the quad-rotor among the civil small unmanned flying objects has gradually increased.
Research into control and induction fields of the quad-rotor has been conducted in advance by many researchers. First, in the control field, there was an attempt to directly control a non-linear system using a back-stepping method or a sliding model method or linearize a quad-rotor model using feedback linearization and then control the quad-rotor model, in order to effectively treat characteristics of a non-linear model of the quad-rotor. In addition, in the induction field, a flip operation for rotating a moving body of the quad-rotor by 360 degrees or more in one side direction was performed or a rapid start-up following a specific trajectory and attitude and an elaborate start-up of exchanging a ball were enabled.
The multi-rotor flying object such as the quad-rotor may be currently controlled and induced precisely due to a contribution of many researches, but still needs to be functionally improved. Considering the fact that an accurate position and attitude of a flying object present on a three-dimensional space are represented by six variables, a multi-rotor flying object system ultimately becomes an under-actuated system in which a dimension of an input is smaller than a dimension of an output. This factor acts as a limitation in the control and the induction of the multi-rotor flying object. For example, a body of the multi-rotor flying object should be necessarily inclined forward in order to accelerate the multi-rotor flying object forward, and an acceleration in a forward direction is not absolutely generated in a state in which the multi-rotor flying object is inclined rearward. That is, it means that an attitude and an acceleration of the multi-rotor flying object may not be completely independent from each other.
Therefore, in the case in which a camera is attached to the body of the multi-rotor flying object to photograph a target, when the multi-rotor flying object changes a direction, the body of the multi-rotor flying object is also inclined, such that a photographing direction of the camera is out of the target to be photographed. In addition, since inclination of the entire multi-rotor flying object is required at the time of changing the direction, responsibility is relatively low, such that a rapid start-up is not easy.